Hi, first of all I'm new here and so I apologise if this has been said before. :-) When looking through the planning application on the councils website, I discovered a page which referred to and showed examples of what would be used for materials for the attraction. Judging by the materials, I personally don't think that the ride could be Harry Potter or DW, but also, why build it there when HP studio's is also in london. Just Speculation anyway....
P.S Since Thorpe Park are hot on Lionsgate movies at the moment, and this style of theming, a hunger games attraction is a possibility.
http://documents.runnymede.gov.uk/AnitePublicDocs/00159366.pdf